Oscillator circuit



May 9, 1939. J. L. POTTER Y 2,157,434

OSCILLATOR CIRCUIT Filed April 17, 1937- A B I T 1 I i/26 I2 I I8 32' 2 3/ is '84- V i: n? 3' j 20 IO FF:

I 3, 22 i L 71 2772? I M yJW v Han/2gp Patented May 9, 1939 UNITED STATES PATENT OFFICE 2,157,434 OSCILLATOR CIRCUIT James L. Potter, Iowa City, Iowa Application April 17, 1937, Serial No. 137,463

7 Claims.

This invention relates to a circuit arrangement adaptable for incorporation in oscillators of the type used to provide a timing axis for cathode ray tubes and the like, or in multivibrator and similar systems.

It is an object of my invention to provide a relatively simple and inexpensive arrangement or combination of parts in a circuit which will perform a sequence of operations in such a peri- ,odic manner as to constitute it an oscillator or the like, and which will eliminate the difiiculty present in other such systems arising from the interaction between the local oscillator and the external circuit used to stabilize or control it, as

16 for example, by regulating the frequency.

It is a further object of my invention to' provide an element of an oscillator circuit which shall have generated across it a highly peaked wave of voltage suitable for biasing a cathode ray tube as used in television to cut-off during the return sweep, thus eliminating the blur or trace.

It is a further object of my invention to provide a simple, inexpensive and reliable means for providing both a linear sweep voltage and, separately, a highly peaked voltage which may be employed for cut-ofi to eliminate the return trace as above set forth.

With these and other objects in view, my invention consists in the arrangement and combination of the various parts of my oscillator circuit, whereby the objects contemplated are attained, 'as hereinafter more fully set forth, pointed out in my claims, and illustrated in the accompanying drawing, in which:

Figure 1 is a diagrammatic representation of a circuit embodying my invention.

Figure 2 is a curve showing the variation in voltage with time across the terminals of the main control condenser or condensers used in my circuit.

Figure 3 is a curve showing the variation in voltage with time between the grid terminal of one of the vacuum tubes'employed in my circuit and ground.

Figure 4 is a curve showing the variation in voltage with time appearing across the common cathode dropping resistor in my circuit.

Figure 5 is a curve showing the variation in voltage with time between the plate of one vacuum tube and ground.

The diagram shown in Figure 1 embodies my invention ina circuit suitable for providing the time axis for deflecting the electron beam in a cathode ray tube, such as is used for ordinary oscillographic purposes and television whereit is desired to have the deflection 'of the beam essentially linear with respect to time. Under most circumstances this requires the application of a potential difference which is also linear with re- 5 spect to time. In the circuit shown in Figure 1, this result is accomplished by charging the condenser lll through a variable resistance I2 from a source of unidirectional current M, which may be a battery, rectifier or other suitable source. 10

The voltage rise across the condenser I0 is essentially linear with respect to time since the condenser charges only to about fifteen per cent or less of its final value. During the charging period of the condenser Ill, the vacuum tube l6 l5 draws no plate current since it is blocked by the nature of the circuit controlling grid of said tube. While the condenser I0 is charging through the variable resistance l2, the condenser l8, which has previously been charged, is gradually dis- 2o charging through the resistance 20 and continues to discharge until the tube [6 starts to draw plate current.

This point occurs when the potential of the condenser Ill and hence the plate to ground volt- 25 age of the tube l6, has reached such a value that the voltage drop across the resistor 20 is no longer sufiicient to bias the tube I6 to cut-off.

The plate current, or discharge current of the condenser l0, which then begins to flow, passes 30 through the resistance 22 and develops thereon a potential of such polarity as to cause a vacuum tube 24 to draw less current, that is, the negative bias on the tube 24 is increased and the plate current consequently is decreased. 35

Inasmuch as the plate current through the tube 24 flows through the resistance 26, a reduction in the current reduces the voltage drop across the resistance 26 and causes the plate end of the resistor 26 to become more positive with respect 40 to ground (see Figure 5). The increased potential between these two points results in the charging of the condenser l8 by current flowing through the resistor 26 and also through the resistor 20. Inasmuch as'the -grid of the tube [6 45 is positive with respect to the cathode during this part of the cycle (see Figure 3) grid current flows and comprises a part of the charge. When the grid of the tube It becomes more positive, the conductivity of the tube increases and it will 50 be seen that the effect is cumulative. When the plate current or discharge current through the tube 16 starts to decrease, due to the decreasing potential difierence across the condenser III, as it discharges, the voltage drop across the resistance 55 22 decreases and the grid potential of the tube 24 shifts positively with respect to the cathode or the cathode becomes more negative with respect to the grid, causing the tube 24 to draw more plate current and the drop across the resistance 26 to increase.

The potential between the plate of the tube 24 and ground is thereby necessarily decreased and because of this decreasedmotential the charge on the condenser l8 decreases. The charge flowing out of the condenser l8 results in a flow of current through the resistance in such a direction that the grid of the tube l6 becomes increasingly negative with respect to the cathode, thereby ultimately blocking the tube l6.

Under these conditions the condenser l0 starts charging again and the process is repeated.

It will be seen that this cycle of operations results in a charging of the condenser I ll by current flowing through the resistance l2 from the source i4. Before the charge progresses to a point at which the charging current would cease to be substantially uniform, the associated circuit operates to render the tube l6 conducting and consequently to act as a shunt or short circuit resulting in the very rapid discharge ofthe condenser In. The cycle is repeated and results in avariation of potential across the terminals of the condenser l0, which is represented by the graph in Figure 2. This is the conventional saw tooth wave of voltage, such as is used to provide a time axis for cathode ray tubes with deflection plates.

Inasmuch as the variation from maximum to minimum of the voltage appearing across the condenser l0 may not be sufilcient for deflection of a cathode ray beam, without some form of amplification, an amplifier may be provided to increase the magnitude of the sweep voltage. The circuit shown in Figure 1 has been divided into two principal parts by dotted lines, that enclosed by the rectangle A being the sweep circuit proper and the portion enclosed in the rectangle B constituting a one stage amplifier suitable for providing the amplification which may be necessary. Any number of stages can be provided in this way.

It will be noted that the circuit is adapted to the use of the so-called hard tubes or high vacuum tubes, as opposed to the soft or gaseous type of tubes. It has been found-that the hard tubes give more satisfactory and consistent operation.

A valuable feature of this circuit as I have shown it is that the voltage occurring across the resistance 22 has the peculiar wave form indicated in Figure 4, having peaks of substantial magnitude but of short duration, in time, .relative to the time between peaks. A periodic peaked wave of this kind may be very useful in certain applications in which a sweep circuit is employed, as for example in television or other cathode ray tube'applications. It is frequently desirable to apply a peaked voltage to the intensity control of the cathode ray tube in such a manner as to extinguish or cut ofl the beam during the return trace. The circuit as I have shown it supplies the linear voltage necessary for transverse sweep purposes, across the condenser lll or the output terminals 28 and 30, and also across the resistor 22, exhibits a peaked voltage such as is shown in Figure 4, which may be applied through suitable amplification devices to the intensity control electrode of the cathode ray tube.

My circuit possesses peculiar advantages as regards synchronizing or interlocking its frequency with that of some external source of periodically recurring or alternating voltage. Such a voltage may be introduced into .the circuit shown by connection to the terminals 32 and 34. It will be observed that the voltage thus applied appears on the grid of the tube 24'.

An advantage of my circuit arrangement over circuits of this type which have heretofore been used, lies in the fact that circuits previously used have applied both the synchronizing and feedback voltage to the grid of the tube and in most cases both of these voltages have been made effective in the grid circuit by passing through the same resistor or impedance. Consequently variations in the electrical characteristics of the external circuit aifect the local oscillator and sometimes cause unsatisfactory operation.

In my circuit the synchronizing potential appears between the grid of the tube 24 and ground. the ground potential being represented by the conductor 36. The feed-back potential, that is, the voltage necessary to cause phase inversion and oscillator operation, appears between cathode and ground, that is across the resistor 22. In my circuit there is no interaction between the grid-ground connection and the cathode-ground connection so that operation of the local oscillator is entirely independent of random or other undesirable changes in the electrical characteristics of the circuit from which. the synchronizing voltage is obtained.

The resistance l2 may be replaced by a vacuum tube such as a constant current pentode to give a constant current charging of condenser l0 and hence a more nearly linear sweep. The two tubes l6 and 24 may be enclosed in the same envelope to reduce the number of tubes and conserve space. This may be accomplished by using duplex triodes in the form of such standard makes as tubes No. 53 and No. 6A6. The tubes 16 and 24 may be either indirectly heated triodes as shown, tetrodes, pentodes, or any tube that functions as above mentioned. Various combinations of the above tubes have been successfully employed. By placing a resistance or other impedance of desired characteristic in series with or in place of the condenser l0, special wave forms may be obtained such as may be required .in connection with electromagnetic deflection, to

which the above circuit may be adapted.

Although I have shown my invention in Figure 1 in a form applicable as a sweep circuit, for use with cathode ray tubes, it is by no means limited to such an application but may be used as a special wave shaping circuit for television, employing the peaked impulses generated across the resistance 22. The same type of circuit with or without the amplifier may be connected in cascade for obtaining multiple impulses or submultiple impulses as a multivibrator circuit, to generate synchronizing voltages for both vertical and horizontal deflection in television.

By removing the condenser l0 and making the resistance l2 a suitable value, the arrangement can be used as a straight multivibrator circuit and when used as such will eliminate the necessity of a bufier tube, inasmuch as there is no interaction between the synchronizing signal and the feed-back, such as occurs with the condenser feed back as used in the standard multivibrator circuit.

Some changes maybe made in the construction and arrangement of the parts of my device with- ,out departing from the real spirit and purpose of my. invention and it is my intention to cover by my claims any modified forms of structure or use of mechanical or electrical equivalents which may be reasonably included within their scope.

I claim as my invention:

1. In a sweep circuit, a condenser, a resistance.

and a source of unidirectional current connected in series, an electron tube, plate, grid and cathode elements in said tube, said plate and cathode elements being connected in series with said condenser, a resistance connected between said grid and cathode elements, a second electron tube, a plate and cathode in said tube, a capacitive coupling of said grid to said plate of said second electron tube, a resistance between said plate of said second electron tube and one terminal of said source of unidirectional current and a com mon resistance in the connection of the cathodes 01. both said electron tubes to the other terminal of said source of unidirectional current.

2. In an electron tube circuit, a source of unidirectional current, a condenser and an impedance, said condenser and said impedance being connected in series with said source, an electron tube, cathode, grid and plate elements therein, a second impedance, said plate and cathode elements and said second impedance being connected in series with said condenser, a third impedance between the grid and cathode elements of said electron tube, a second electron tube, cathode and plate elements therein, a fourth impedance coupling said grid of said first mentioned tube to said plate of said second electron tube, and a filth impedance connected between the plate of said second electron tube and said source of unidirectional current, said cathode of said second electron tube being connected to one terminal of said second impedance, and said source of unidirectional current being connected to the other terminal oi said second impedance.

3. The combinaion of a condenser, means for charging said condenser from a source of current at a substantially constant rate, a vacuum tube having at least three elements therein, its platecathode circuit being connected across said condenser, an oscillator circuit connected to the grid 01' said tube for maintaining said grid highly negative during the charging interval of said condenser and means in the oscillator circuit for rapidly driving said grid positive to discharge the condenser at predetermined intervals, said oscillator circuit comprising a second vacuum tube, the plate of said second vacuum tube being connected to the grid of said first mentioned vacuum tube through a condenser, and an impedance, the cathodes of said second vacuum tube and said first mentioned vacuum tube being both connected through said impedance to a source of suitable current.

4. A combination of a condenser, a source of current, means for charging said condenser from said source, a vacuum tube having at least three elements therein, its plate-cathode circuit being connected across said condenser and an oscillator circuit connected to the grid of said tube for controlling the potential 01 said grid relative to the cathode of said tube, said oscillator circuit comprising a second vacuum tube, the plate of said second vacuum tube beingcoupled to the grid of said first mentioned vacuum tube, and the oathodes of said tubes being connected together, a resistance between said cathodes and one terminal of said source, and a potentiometer having one end terminal connected with said one terminal of said source and having an intermediate terminal connected with the grid of said second tube.

5. In a sweep circuit, a condenser, a resistance and a source of unidirectional current connected in series, an electron tube, plate, grid and cathode elements in said tube, said plate and cathode elements being connected in series with said condenser, a resistance connected between said.- grid and cathode elements, a second electron tube, plate, grid and cathode elements in said second tube, a capacitive coupling of said grid of said first tube to said plate of said second electron tube, a resistance between said plate of said second electron tube and one terminal of said source of unidirectional current, a connection between the cathodes of said tubes, a resistance between said connection and the other terminal of said source and a potentiometer having one terminal connected with said other terminal of said source and another terminal connected to said grid of said second electron tube.

6. In a multivibrator circuit, an electron tube, plate, grid and cathode elements therein, a source of unidirectional current, a resistance between the plate of said tube and one terminal of said source of unidirectional current, a resistance between cathode and grid terminals of said tube, a second electron tube, plate and cathode elements therein, a condenser coupling the grid of said first tube to the plate of said second tube, a resistance between the plate of said second tube and said one terminal of said source of unidirectional current, a resistance having one end connected to the cathodes of both said tubes and its other end connected to the other terminal of said source of unidirectional current, and a second condenser having one terminal thereof connected to the plate of said first tube and its other terminal connected to said other terminal of said source of unidirectional current.

7. In an oscillator circuit, a condenser, a current limiting device and a source of unidirectional current in series, an electron tube, cathode, grid and plate elements therein, an impedance, said plate and cathode elements and said impedance being connected in series with said condenser, a second impedance between the grid and cathode elements of said electron tube, a second electron tube, cathode and plate elements therein, a condenser coupling said grid of said first mentioned tube to said plate of said second electron tube, a third impedance connected between the plate of said second electron tube and said source of unidirectional current, and a connection between the cathode of said first mentioned tube and the cathode of said second tube.

JAMES L. PO'I'I'ER. 

